Electronic devices



y 14, 1959 R. MILLERSHIP 2,895,075

7 ELECTRONIC DEVICES Filed Dec. 12, 1956 1 2 Sheets-Sheet 1 R.MILLERSHIP ELECTRONIC DEVICES July 14, 1959 Filed Dec. 12, 1956 2 sheets-sheet 2 15 FIG.8.

FIG.7.,

wnnn-wnnnnnnnnnnn-w United St ws Patent 2,895,075 ELECTRONIC DEvitiEsiRonald Millership, London, England, assignoito Elliott Brothers(London) Limited, London, England, 'a British company H ApplicationDecember 12, 1956, Serial No. 627,796 Claims priority, application GreatBritain December 12, 1955 22 Claims. (Cl. 315-39) This invention relatesto improvements in electronic devices and is particularly concerned withimprovements in devices of the kind (hereinafter referred to as being ofthe.kind specified?) adapted to be inserted into a waveguide to extractenergy therefrom and to provide an indication of the magnitude of theenergy propagated through the waveguide. and comprising anfevacu'atedenvelope, which may or may notcontain a vapour or gas at a low pressure,in which is disposeda cathode arranged axially within a cylindricalanode to provide a co-axial transmission line, the cathode. extendingb'eyond'at least one end of the anode and a transformer associated withsuch extension of the cathode adapted to transform the mode of theenergy propagated through the waveguide to a mode for propagation alongthe coaxial transmission line provided by the anode-cathode structure.

, In such devices it is desirable that the minimum amount of energyshould be reflected back along the waveguide and also that the minimumamount of energy should be reflected back from the end of the co-axialline remote from the input waveguide. vIt has been proposed to achievethe latter by extracting the energy from the device after it is passedalong the coaxial line by the provision within the device of a furthertransformer which is adapted to transform the mode of the energypropagated along the co-axial line into an appropriate mode fortransmission along a further waveguide and to' associate with the deviceand this further transformer such a further waveguide which is suitablyarranged to absorb the energy with the minimum of reflection afterit'has been propagated through the coaxial line. Such'known devicessuffer from the disadvantage that they require to be associated with afurther waveguide as referred to above and the task of replacing adevice is made tedious and time consuming by the necessity of removingthe further waveguide from its association with the device before thelatter can be'removed from the first mentioned waveguide along which theenergy to be measured is being propagated.

it is an object of the present lnvention to provide an improvedelectronic device of the kind specified which :shall not require to beassociated with a further waveguide, which may readily be inserted intoor removed from a wave-guide along which the energy to be measured ;isto be propagated, and which shall be economic ,to

manufacture. I

The present invention broadly stated comprises an electronic device ofthe kind specified wherein the cathode is surrounded by a body of lossydielectric material at a location spaced from the transformer in thedirection .in which the energy is to be propagated along the coaxialline constituted by the anode cathode structure.

Preferably the material is arranged to produce the minimum reflectionalong the .co-axial line towards the transformer.

In a preferred embodiment of the present invention the :cathode extendsbeyond the cylindrical .anode in the direction in which energy is to bepropagated along the co-axial line and the envelope is surrounded by asleeve oflossy dielectric material which has one end containedsubstantially in the plane containing the end of the anode remote2,895,075 Patented July 14, 1959 ICC . 2 from the transformer andextends away therefrom in the direction of propagation of energy alongthe co-axial line.

It is preferred to taper the sleeve at its said one end andadvantageously the radial thickness of the sleeve increase graduallyfrom the said one end towards its other end.

The term lossy dielectric material as used herein is defined as meaninga material having a large magnetic and/ or electric loss angle.

In order that the invention may be clearly understood some'embodimentsthereof will now be described by way of example reference being made tothe accompanying drawings in which:

Fig.1 is a part-sectional part-elevational view of a device according tothe invention showing it associated with a waveguide through which theelectromagnetic energy to be measured is to be propagated,

Fig. 1A is a section taken on the line IAIA of Fig. 1, I Fig. 2 is aplan view of an element shown in Fig. l,

and

-Figs. 3 to 8 are fragmentary sectional views illustrating modificationsof the device of Fig. 1.

In the first example illustrated in Fig. 1 the device comprises a hollowtubular cathode 1 which extends coalxially through a cylindrical anode2, the axial length of the'cathode 1 being greater than that of theanode2 so that the cathode 1 is surrounded by the anode 2 for only a part ofits length intermediate its ends. The cathode 1 and the anode '2constitute a .co-axial transmission line and are enclosed in anevacuated glass envelope formed in twoco-axial substantially clindricalparts indicated at 33; and. 3b. The anode 2 Which. is shown in elevationin Fig. 1, is supportedlwithin the envelope by means of a thin metalsleeve 4 which is in electrical contactwith the anode 2 and has anannular flange 5 which is slightly dished at its periphery and which isconnected at its periphery to a surrounding annular element 5a by fourequi-angularly spaced radial arms 5b (as can be seen more clearly inFig. 2) which are sufliciently flexible to permit the annular element 5ato move slightly in the axial. direction relative to the annular flange5. The flange 5 extends between the adjacent ends of the parts 34 and 3bwhich, are sealed on to the flange 5, the latter together with theannular element 5a providing an electrical connection externally of theenvelope for the anode Q4. One end of the cathode 1 which extends beyondthe one end of the anode 2 in the envelope part 3b extends .through atransformer 6 of known construction and is electrically connectedthereto and is located and sup ported thereby. This end of thej cathode1 is sealed into a glass seal (not shown) which closes the end of theenvelope. part 3b remote from the part 3a. The other end of the cathode1 extends for some distance beyond the other end of the anode 2 withinthe envelope part 3a and is.;supported and located by .a spider element7. This end of-the cathode 1 is pinched on to the end of a heater ,coilfinot shown) which extends through the cathode 1 throughout the lengththereof and which is electrically connected .bymeans of the lead 8 tothe metal cap 9 which covers theclosed end of the envelope 3b. Thepinched end .of the cathode 1 is secured to an element 10 which isconnected by means of a spring 11. to a similar element 12, secured to apin 13 which extends through the closed endof the envelope part 3a. Theelements 10 and 12 are electrically conducting and are electricallyconnectedto each other by a flexible lead 14 so that the cathode 1 iselectrically connected to the pin 13. The spring 11 accommodates anyvariation in the length of the cathode 1 which occur in use due, forexample, to temperature variations.

LA: metal'sleeve 15, e.g. of copper, of hollow frusto- 'conical'for'm',having at its smaller end an internal diam.

eter slightly greater than the external diameter of the envelope part3a, is slipped over this part with its smaller end leading until theplane containing the smaller end is substantially coincident with theplane containing the end of the anode 2 remote from the transformer 6.The axial length of this sleeve is such that in this position its largerend extends a short distance beyond the closed end of the envelope part3a. The space between the inner surface of the sleeve 15 and the outersurface of the envelope part 3a is then filled with a lossy dielectricmaterial indicated at 16. This material is preferably composed offerromagnetic dust in a binding medium such as polymerised resin whichmay, or may not, be expanded. A material which has been found to beespecially suitable is a suspension of fine carbonyliron dust in abinding medium such as that sold under the trade name of Marco Resin, inequal proportions by weight. This suspension of fine conductingparticles in a binding agent constitutes a dielectric material having ahigh dielectric constant and large magnetic and electric loss angles,whose properties can be controlled by variation in the proportions ofmagnetic material present in the'dielectric material and by variationsin the particle size of the magnetic material together with a selectionof magnetic material having suitable conductivity and magneticproperties. The lossy dielectric material 16 maybe introduced into thespace between the sleeve 15 and the envelope part 3a in a fluid orsemi-fluid state, and then caused or allowed to set or it may beintroduced in a finely divided powdered form and caused to assume acoherent solid state. The larger diameter end of the sleeve 15. is thenclosed with a metal disc 17 having a central aperture which receives theouter end of "the pin 13 which is then electrically connected thereto,e.g. by solder. The disc 17 is in electrical contact with the sleeve 15so that the latter is in electrical contact with the cathode 1 and theend of the coiled heater remote from the lead 8.

Four fins 18 (of which only two can be seen in Fig. 1) are secured tothe outer surface of the sleeve 15 for the purpose of dissipating heatand are arrangedto extend radially from the sleeve 15 being disposed at90 intervals around the latter. The outer longitudinal edges of the fins18 extend substantially parallel to the axis of the cathode 1 and theaxial length of the fins 16 is such that they extend from the largerdiameter end'of the sleeve 13 to within a short axial distance of theflange 5. The fins are cutaway as at 19 adjacent to the smaller diameterend of the sleeve 15 and they are secured to or 1 formed integrally withan annular member 20 adjacent to the flange '5. The face of the member20 remote from the fins 18 is recessed slightly as at 23 to receive awasher 24 of insulating-material which stands ,above this face of thedisc and bears against the annular element'Sa. The recessed face ofthe-member 20 is formed witha shallow radial groove 21 of relativelysmallwidth. A cup-shaped nut-member 25 is provided having an aperture 26formed in its base of a diameter to permitfthe member 25 'to be slippedover the fins 18 but such that it will engage the-annular member 20. Thecylindrical wall of'this member 25 is threaded internally soas to becapable of engaging an annular member '27 which is threaded externallyand which forms part of ach'oke block indicated generally at 28. Thechoke block 28 surrounds a part of -the length of therectangular-section waveguide 29 through which the energy to be measuredis to be propagated, and has one wall 30 through which a plug 31 foraco-axial cable extends and-two side walls 32 and 33 which flankthe'wider walls of the waveguide 29. The walls 32 and '33 and theassociated wallsof the waveguide 29fare formed with circular apertures"to provide passages 34 and 35 respectivelythrough which the envelopepart Sb'may extend with'clearance. Secured to the outer face of the wall32 is an annular m'e'fnber 36 having an'annular'recess 37 on its innerface.

The face of the annular member 27 presented to the wall 33 is formedwith an annular recess 38. The axial lengths of the passages 34 and 35and the radial width of the respectively associated recesses 37 and 38are selected to be such that when the device is inserted through thepassages 34 and 35 so that the plane containing the end of the anode 2adjacent to the transformer 6 is substantially co-planar with the innersurface of one of the wider walls of the waveguide 29 and thetransformer 6 extends through the opposite wall of the waveguide; thepassage 34 and the recess 37 will provide an effective short-circuitbetween the transformer 6 and the associated wall of the waveguide 29and the passage 35 and the recess 38 will provide an effectiveshort-circuit between the anode 2 and the associated wall of thewaveguide.

The outer face of the member 27 is formed with an annular recess39'having an outer diameter substantially equalto'that of the recess 23.This recess 39 is lined with a cup-shaped washer 40 of insulatingmaterial within which isdisposed a metal ring 41 connected by aninsulated lead 42 'to the pin 43 of the plug 31 for connecti'ont'o theinner conduct'or of a co-axial cable. The wall of the memberf27 boundingthe recess 39 is formed with aradial 'slot 39a to accommodate the lead42 and the washer 40 is formed with a radial slot 40a which isarrangedas a continuation of the slot 39a so that the lead 42 extendsthrough the slot 40a to the ring 41.

When "it 'is desired to insert a device constructed as desefibed aboveinto the waveguide 29, the device is passed thrdugh'the passages 35 and34 with the cap '9 leadiii'gffintil the annular element 5a connected tothe flahge'Sfisbroiight up against the metal ring 41. The fiiut'nieinber'25 is thentightene'd onto the annular memberf 27 sothattheflang'e 5 andthe ring 41 are sandwiched ibetweeh fthe washers '24 and 40. V Theflange 5 is then connected electrically to the pin 43. The slight amountof: relativeaxi'al movement which is possible between the annularelement '54 and the flange 5 due to the radial arins 5b prevents theseal 'between the envelope parts 3a am 3b and the flange 5 being brokenwhen variations in the axial lengths of the envelope parts 3a and 3b andthe 'fi'ns 18 occur due to temperature variations. The dimensions of thevarious members are such that when the annular e'leiririt'Sdbearsagainst the ring 41 the end of f'the anodel adjacent the transformer 6is substantiallyco-planar with the inner surface of one'wall of thewaveguide and the transformer 6 extends through the fopposite'wa'll ofthe waveguide 29 to the interior of the latter.

In the operation of the device the electromagnetic energy 'propag'atedalong the waveguide 29is transformed into "the appropriate mode and ispropagated along the ,co-axial line provided by the anode-cathodestructure. v'vill be understood an adjustable matching plunger fmaybefp'rovided'in'the'waveguide 29 on the side of the deviceremote'fromthe source'of the energy'to prevent "reflections. The anode 2acquires a potential which is a function "of themagnitude of the energypropagated "along thewaveguide 29 and this appears at the pin 43 whichmay be connected by a coaxial cable to one of the plates ofa cathode-raytube where thispotential can 'b'e u's'ed to'give'a visualtrace theamplitude of which is a fu'notionof'the magnitude of the energypropagated alongfthe 'wavegide'2 9, The energy propagated along the"co'axialline coristituted'by the anode-cathode structure isfgr'adually'absorbed by the lossy dialectric material '16f'as it lpassesthrough theplane containing the -eridofthe"anode '2'remote f'rom the transformer 6.Due to the fact that the lossy dielectric material '16 comfmences'at'this'plane and its radial'thickness. gradually increases in the'direction of propagation, the minimum nt of energy isreflected backto'the anode-cathode uctiire, The axial; length 'of'the sleeve of lossydiniatfial isYpreferably 'made such that'it will absorb substantiallyall of the energy delivered from the anode-cathode structure. Q

It will be readily appreciated that the lossy dielectric material 16need not necessarily be arranged as described above with reference toFig. 1. The only essential feature is that it should surround thecathode and should absorb atleast a proportion of the electromagneticenergy after propagation through the anode-cathode structure.Alternative arrangements are illustrated in Figs. 3 to 7 in whichthelossy dielectric material is disposed within the envelope part 3a and.in Fig. 8 in which the lossy dielectric material is disposed externallyof the envelope part 3a in a manner somewhat similar to that shown inFig. 1.

In the arrangement illustrated in Fig. 3 the end of the anode 2 remotefrom the transformer 6 (not shown) is flared gradually outwards as at 2aand the space between the inner surface of the flared portion 2a and animaginary continuation of the inner surface of the cylindrical part ofthe anode 2 is filled with the lossy dielectric material 16 which willabsorb the energy propagated along the anode-cathode structure with theminimum of reflection.

In the arrangement illustrated in Fig. 4 the anode 2 is again flaredoutwards as indicated at 2a and in this example the cathode 1 is alsoflared outwards as at 1a to provide an annular space between the anode 2and cathode 1 and the parts 2a and 1a which has a constant radialdimension throughout its length. The space bounded by the inner surfaceof the part 2a, the imaginary extension of the cylindrical part of theanode 2 and a part of the part 1a is filled with lossy dielectricmaterial 16.

In the arrangement illustrated in Fig. 5 the lossy dielectric material16 surrounds the cathode 1 within the anode 2 and is in the form of aconical plug coaxial with the cathode 1 which has a diameter at its baseequal to the diameter of the anode 2 so as to close the end of thelatter remote from the transformer 6 (not shown).

' In the arrangement illustrated in Fig. 6 the end of the cathode 1 at alocation adjacent to the end of the anode remote from the transformer 6(not shown) is gradually reduced in diameter and this tapered end issurrounded by a body of dielectric material 16 of gradually increasingthickness such that the outer surface of the material 16 forms acontinuation of the outer surface of the cathode 1.

' In the arrangement illustrated in Fig. 7 the lossy dielectric material16 is in the form of a cylindrical plug which closes the end of thecylindrical anode 2 remote from the transformer 6 and which at its innerend is formed with a conical recess 16a such that the energy propagatedalong the anode-cathode structure encounters an increasing thickness ofthe material.

The arrangement illustrated in Fig. 8 is similar in many respects tothat illustrated in Fig. l, the frustoconical sleeve 15 of that examplebeing also employed in this arrangement. A short distance from theadjacent end of the anode 2 of the cathode 1 is flared outwards as at laand then merges into a cylindrical body portion 1b which supports thecathode within the envelope. The wall of the flared part 1a is continuedexternally of the envelope by a frusto-conical metallic sleeve 15asimilar to the sleeve 15 and the space bc tween the sleeves 15 and 15ais filled with lossy dielectric material. The cathode 1 is shown in Fig.8 in elevation with the flared part 1a and the cylindrical body portion111 shown largely in section.

As will be understood an electronic device according to thisinvention isused to extract energy from and to provide an indication of themagnitude of the energy propagated through a waveguide by inserting thedevice into the waveguide in the manner illustrated in Fig. 1 so thatthe energy propagated along the waveguide is transformed 'by thetransformer=6and propagated along the co-axial transmission lineconstituted 'by the cathode 1 and the anode 2. As described the cathodeis heated and emits electrons which are-subjected'to the fields ofelectromagnetic energy propagated along the co-axial transmission line.Due to the electrons reaching the anode 2 the latter acquires a negativepotential with respect to the cathode, and owing to the effect of theenergy propagated along the transmission line on the flow of theseelectrons, the magnitude of the potential acquired by the anode is afunction of the magnitude of the energy propagated through the waveguideand provides a measure thereof.

What I claim is:

1. An electronic device of the kind adapted to be inserted into awaveguide to extract energy therefrom and to provide an indication ofthe magnitude of the energy propagated through the waveguide, comprisingan evacuated envelope, a cylindrical anode disposed within the envelope,a cathode arranged co-axially within the anode to provide a co-axialtransmission line, the cathode extending beyond at least one end of theanode, a transformer associated with such extension of the cathode anddisposed wholly within the envelope and adapted to transform the mode ofenergy propagated through the waveguide to a mode for propagation alongthe co-axial transmission line and a body of lossy dielectric materialsurrounding the cathode at a location spaced from the transformer in thedirection in which the energy is to be propagated along the co-axialtransmission line.

2. A device according to claim 1 wherein the cathode extends beyond thecylindrical anode in the direction in which energy is to be propagatedalong the co-axial line and said body is in the form of a sleevesurrounding said envelope and having one end contained substantially inthe plane containing the end of the anode nemote from the transformerand extending away therefrom in the direction of propagation of energyalong the co-axial line.

3. A device according to claim 2 wherein the radial thickness of saidsleeve increases gradually from the end thereof nearest said transformerfor at least a part of its length.

4. A device according to claim 1 wherein the body of material isdisposed within the envelope.

5. A device according to claim 4 wherein the end of the anode remotefrom the transformer is flared outwards and the body of materialsubstantially fills the space between the inner surface of the flaredportion of the anode and an imaginary continuation of the inner surfaceof the cylindrical part of the anode.

6. A device according to claim 4 wherein the end of the anode remotefrom the transformer is flared out- 'wards, the cathode, which for themajor part of its length is tubular, has its corresponding end similarlyflared to provide an annular space between the anode and the cathodewhich has a constant radial dimension throughout its length and saidbody of material substantially fills the space bounded by the innersurface of the flared part of the anode, an imaginary continuation ofthe cylindrical part of the anode and a part of the flared part of thecathode.

7. A device according to claim 4 wherein the body of material is in theform of a substantially conical plug which is disposed within the anodeand surrounds and is co-axial with the part of the cathode, the largerdiameter end of the plug closing the end of the anode remote from thetransformer.

8. A device according to claim 4 wherein the end of the cathode at alocation adjacent to the end of the anode remote from the transformer isgradually reduced in diameter and the body of material surrounds thistapered end of the cathode in a gradually incneasing thickness such thatthe outer surface of the material forms a continuation of the outersurface of the cathode. 9. A device accordingto claim 4 wherein the bodyof material is in the form of a cylindrical plug disposed within theanode and which closes the end thereof from the transformer, the innerend of the plug being formed with a conical recess such that theenergyprop'agated along the anode-cathode structure encounters anincreasing thickness of the material.

10. A device according to claim 1 wherein the envelope is in two partsand the anode is supported within the envelope by a thin metal sleevehaving an annular flange which extends between adjacent ends of saidenvelope parts said adjacent ends being sealed on to said flange.

11. A device according to claim 10 wherein said flange is slightlydished.

12. A device according to'claim 10 wherein said flange is connected to asurrounding annular element by arms which are sufficiently flexible topermit slight axial movement of said annular element relative to saidflange.

13. A device according to claim 1 for use in association with awaveguide of rectangular cross-section and having associated therewith achoke block comprising two side walls adapted to flank the Wider wallsof the waveguide and each formed with a passage through which theenvelope extends with clearance, and an annular member secured to theouter face of each side wall and formed on its inner face with anannular recess, the length of the passage in each side wall and theradial widthof the annular recess in the associated annular member beingselected to be such that when the device is inserted through thepassages so that the plane containing the end of the anode issubstantially co-planar with the inner surface of one of the wider wallsof the waveguide and the transformer extends through the opposed widerwall of the waveguide, one passage and annular recess provide aneffective short-circuit between the transformer and the associated widerwall of the waveguide and the other passage and annular recess providean effective short-circuit between the anode and the associated widerwall of the waveguide.

14. An electronic device of the kind adapted to be inserted into awaveguide to extract energy therefrom and to provide an indication ofthe magnitude of the energy propagated through the waveguide, comprisingan evacuated envelope, a cylindrical anode disposed within saidenvelope, a cathode disposed coaxially within said anode to provide aco-axial transmission line and extending at each end beyond said anode,at least that part of said envelope surrounding the extension of thecathode beyond one end of the anode being of substantially uniformcircular cross-section, a transformer disposed wholly within saidenvelope and associated with the extension of the cathode beyond theother end of the anode and adapted to transform the mode of energypropagated through said waveguide to a mode for propagation along saidco-axial transmission line, a hollow frusto-conical metal sleevesurrounding said part of said envelope with its smaller diameter endcontained substantially in a plane containing said one end of saidanode, and a body of lossy dielectric material substantially filling thespace between said part of said envelope and said metal sleeve.

15. A device according to claim 14 wherein a number of fins are securedto the outer surface of the metal sleeve for the purpose of dissipatingheat.

16. A device according to claim 15 wherein the fins are equiangularlyspaced about the axis of the metal sleeve.

17. A device according to claim 15 wherein the outer longitudinal edgesof the fins extend substantially parallel to the axis of the cathode.

18. A device according to claim 15 wherein the axial length of the finsis such that they extend beyond the smaller diameter end of the metalsleeve towards the transformer.

19. A device according to claim 18 wherein an annular member is securedto or integral with the ends of the 8 fins nearest to' the transformer,this annular member providing a means whereby the device may be coupledto a choke'block.

20. An electronic'device of the kind adapted to be inserted into awaveguide to extract energy therefrom and to provide an indication ofthe magnitude of the energy propagated through the waveguide, comprisinga substantially cylindrical evacuated envelope, a cylindrical anodedisposed within said envelope, a cathode disposed co-axially within saidanode to provide a coaxial transmission line and extending at each endbeyond said anode, a 'transforrn'er'disposed wholly within said envelopeand associated with the extension of the cathode beyond one end of saidanode and adapted to transform the mode of energy propagated throughsaid waveguide to a mode for propagation along said co-axialtransmission line, a hollow frusto-conical metal sleeve surroundingthat'part of said envelope in which is disposed the extension of thecathode beyond the other end of said anode, said "metal sleeve beingdisposed with the smaller diameter end thereof substantially containedin a plane containing said other end of said anode and extending awayfrom said transformer the axial length of said metal being such that thelarger diameter end thereof extends a short distance beyond one end ofsaid envelope, a body of lossy dielectric material substantially fillingthe space between saidmetal sleeve and saidenvelope, a metal discclosing said larger diameter-end of said metal sleeve and an "electricalconnection from said metal disc to said cathode.

21. A device'acc'ordin'gto claim 20 wherein said elec trical connectionincludesa pin'extending through said envelope and electrically connectedto said metal disc arids'aid cathode.

22. An electronic device 'of the kind adapted to be inserted into awaveguide to extract energy therefrom and to provide an indication ofthe magnitude of the energypropagated through the waveguide, comprisingan evacuated envelope, acylind'rical anode disposed within saidenvelope, 'a cylindrical cathode disposed co-axially within said-anodeto provide a co-ax-ial transmission line and extending at each endbeyond said anode, at least that part of'saidenvelope surrounding theextension of the cathode beyond one endof the anode being ofsubstantially uniform'circular c'ross-section and the exten sion of saidcathode within said part of said envelope being flared conicallyoutwards to merge into a cylindrical body portion which supports saidcathode within said envelope,-a transformer disposed wholly within saidenvelope and associated with the extension of said cathode beyond theother end of said anode and adapted to transform the mode'of energypropagated through said waveguide to a mode for propagation along saidco-axial transmission line, two similar hollow frusto-conic'al metalsleeves co-axially disposed around said part of said 'e'n'evl'o'pe inspaced relationship with the smaller diameter end of one substantiallycontained in a plane containing said one end 'of said anode and thesmaller diameter end of the other sleeve spaced therefrom on the sideremote from said other end of said anode, said other sleeve beingarranged'as ac'o-ntinuation of said flared conical "part'of said cathodeand a body of lossy dielectric material substantially filling theannular space between the two metal sleeves.

References Cited in the file of this patent UNITED STATES PATENTS1,971,902 Claviera Aug. 28, 1934 2,122,538 Potter July 5, 1938 2,129,712Southworth Sept. 13, 1938 2,433,074 Tuller Dec. 23, 1947 FOREIGN PATENTS

